Chromium complexes monodentate

On the basis of spectroscopic data and elemental analyses, the bis-tin adducts were characterized as containing the dianionic units, [cis-(Ph3Sn)2M-(CO)4]2 (Table VI), whereas [(Ph3Sn)3Cr(CO)4] was established to contain seven-coordinate chromium by a single-crystal X-ray study (100). The latter compound was the first seven-coordinate chromium complex to contain only monodentate ligands (Fig. 16). 

Monodentate [O] compounds, chromium complexes, 5, 351 Monodentate iV-heterocyclic carbenes, with silver(I) complexes, 2, 206 Monodentate ligands... 

Copper complexes of azo dyes are used widely in both reactive dyes (Chapter 8) and direct dyes (Chapter 7) for cellulosic fibres. In these dyes, the copper complexes adopt four-coordinate square planar geometry, with the three coordinating sites of the dye occupying corners of the square and the fourth occupied by a monodentate ligand, commonly water (Figure 3.6). The most important cobalt and chromium complexes of azo dyes adopt six-coordinate octahedral geometry, with the six positions occupied by coordination with two... 

Ofele and Herberhold explored the coordination chemistry of NHC with chromium tetra-carbonyl- and penta-carbonyl-chromium complexes more than 40 years ago [5,73]. Since then, several complexes of the general formula (NHC)Cr(CO)5 or (NHC)2Cr(CO)4 have been structurally characterized [74-78]. A variety of monodentate Cr-NHC adducts (with various oxidation states for the chromium center) have also been synthesized and characterized. For instance, the reactivity of NHCs with chromium (II) metallocene complexes has been studied. The reaction of chromocene with imidazolium chloride was reported to afford 14-electron Cr (II) complexes of the type CpCr(NHC)Cl 50 via a CpH elimination reaction (Scheme 14.26), isolated as highly air sensitive species [79,80]. Oxidation of the latter with PbCl2 (when NHC = PPr) or with CHCI3 (when NHC = IMes) produced the corresponding Cr (III) NHC dichloro... 

Thiocarbamate (tc, RHNCSO-) is a monodentate ambidentate ligand, and both oxygen- and sulfur-bonded forms are known for the simple pentaamminecobalt(III) complexes. These undergo redox reactions with chromium(II) ion in water via attack at the remote O or S atom of the S- and O-bound isomers respectively, with a structural trans effect suggested to direct the facile electron transfer in the former.1045 A cobalt-promoted synthesis utilizing the residual nucleophilicity of the coordinated hydroxide in [Co(NH3)5(OH)]2+ in reaction with MeNCS in (MeO)3PO solvent leads to the O-bonded monothiocarbamate, which isomerizes by an intramolecular mechanism to the S-bound isomer in water.1046... 

A number of chromium(III) complexes containing monodentate amine ligands are known and details of their electronic spectra are given in Table 48. 

Ligand exchange reactions of monodentate amides, iodides, or alkoxide complexes with other amides, alkoxides as well as sulfides, and carbon ligands has been documented [23,25]. A rather unique reaction of a trimethylsilylmethyl ligand bound to a chromium nitride has been reported thus, reaction of tert-butyl isocyanide with 52 is reported to furnish 53 (Eq. (17)). 

The ammonia and amine complexes are the most numerous chromium derivatives and the most extensively studied. They include the pure ammine [CrAm6]3+, the mixed ammine-aqua types, that is, [CrAm4 (H20) ]3+ (n = 0-4, 6), the mixed ammine-acido types, that is, [CrAm6 X ](3" )+ (n = 1-4, 6), and mixed ammine-aqua-acido types, for example, [CrAm6 m(H20) Xm](3 m7+ (here Am represents the monodentate ligand NH3 or half of a polydentate amine such as ethylenediamine, and X an acido ligand such as halide, nitrite, or sulfate ion). These complexes provide examples of virtually all kinds of isomerism possible in octahedral complexes. 

The chromium carbonyl complexes with one monodentate and one bidentate ligand in System 8 show systematic changes in F ,i and F ,2 (but in opposite directions), when the ligands are changed from a P—P to a P—As and an As—As type (for -dpadpe the coordination to Cr is through P ). The first, chemically reversible oxidation is made easier in going from dppe to dpae, while the second, chemically irreversible oxidation becomes increasingly more difficult. The one-electron oxidation products slowly decompose to trons-[Cr(CO)2( -L-L)2]+ - . 

We have reported the synthesis and the characterisation of a new series of the polynuclear complex compounds of iron(iii) and chromium(in) where the bridging ligand is squarate dianion, coordinated in a /i-l,3-bis(monodentate) manner. 

Observations on the reaction of ethylmalonatopentaamminecobalt(III) with Cr(H20)g + introduce a new element of interest. The chromium(III) products are the chelated malonate (67%) with a corresponding amount of free alcohol and the monodentate ester complex (33%). Since ester hydrolysis in the latter species is slow, we conclude that hydrogen results from the ester in the chelate form. Again, since ring closure of the monodentate product complex is slow, chelation must have occurred before Cr is oxidized to Cr . It is possible that formation of the chelate as primary product is complete, and that this product reacts in part to yield the monodentate product before hydrolysis occurs. Activation based on electron transfer to trap a function which is sensitive to a substitution-inert metal ion acting as a Lewis acid could presumably be extended to other more interesting situations. 

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